The present invention relates to a heating apparatus provided with a weight sensor for measuring the weight of one or more food items which are a material to be heated and a gas sensor for detecting the amount of change of a physical parameter such as, for example, gas or vapor generated from the food material being cooked and, more particularly, to an automatic cooking apparatus for cakes to be baked in an oven.
A heating apparatus capable of controlling the length of heating time automatically is currently widely utilized. For example, an automatic electronic range having an oven function is rated highly of its convenience and heavily occupies the market of heating and cooking apparatuses. However, the conventional oven cooking, for example, automatic cooking of cakes, cookies, cream puffs and others, is carried out by detecting the temperature in a heating chamber with the use of a temperature sensor such as a thermistor, then measuring the time elapsed from the start of heating until the temperature inside the heating chamber attains a controlled temperature, and multiplying the elapsed time by a certain constant to determine the total heating time.
More specifically, the conventional oven cooking employs a control sequence wherein the temperature inside the heating chamber, in which the food material is placed, by the use of a temperature sensor such as a thermistor, the time T.sub.1 required for the temperature inside the heating chamber to attain a controlled temperature subsequent to the start of heating is then measured by the use of a timer, the time T.sub.1 is multiplied by an artitrarily chosen constant k, and finally a predetermined heating time A is added to the product of the time T.sub.1 times the arbitrary constant k, i.e., A+k.multidot.T.sub.1, thereby to give the total heating time during which the food material is heated.
Although the conventional heating apparatus utilizing this control sequence can accommodate, to a certain extent, change in environment (temperature and so on) and/or power source voltage, it has the following problems.
(1) Since a particular base heating time A and a particular constant k are allocated to each automatic cooking key, one automatic cooking key cannot be used for cooking different items of a menu. By way of example, when it comes to a cake, there is a variety of cakes, such as, for example, sponge cake, bundt cake, batter cake and so on, each requiring a different heating time. Therefore, types of cakes acceptable to the conventional automatic cooking are limited. PA1 (2) When the amount of material to be cooked changes, it cannot be properly cooked. Since both the base heating time A and the constant k are fixed, the conventional heating apparatus works satisfactorily with specified amounts illustrated in a cookbook available as an accessory to the heating apparatus. For example, if the amount is decreased to half the specified amount, excessive baking occurs, but if it is increased to twice the specified amount, insufficient baking occurs. PA1 (3) A vessel usable in the conventional heating apparatus is limited in shape. Particularly, in the case of cake making, the required heating time varies with the shape of a vessel. For example, the use of a shallow vessel with large opening area requires a smaller heating time than the use of a deep vessel with small opening area. The conventional heating apparatus cannot accommodate changing shapes of vessels, and the shape of the vessel usable therein is limited.
As hereinabove discussed, the conventional automatic heating apparatus for oven cooking has limited applications as to the type, the amount and the shape of a vessel useable. In order to obviate these limitations, the present invention makes use of a weight sensor and a gas sensor.
Although a means for carrying out an automatic cooking by the combined use of the weight and gas sensors is utilized in a warming mode of the automatic cooking utilizing a mirowave heating technique, the manner in which it is used will be described hereinafter. Simultaneously with the start of cooking, the weight of the food material is measured by the weight sensor, and a time limit of the cooking appropriate to the measured weight is set. The greater the weight, the longer the heating time and, therefore, the time limit is so set as to be long. At the same time, measurement of vapor produced by the food material is also performed by the gas sensor, and, at the time the level of vapor so measured has attained a predetermined detection level, the total cooking time is fixed on the basis of the time elapsed from the start of cooking and until the level of vapor so measured attains the predetermined detection level. Then, the cooking time determined upon the detection by the vapor sensor and the time limit determined by the weight sensor and appropriate to the particular weight are compared, and the cooking terminates upon the passage of one of the times which is smaller than the other. Although in the case of warming of most food materials, the cooking time is determined by the gas sensor, excessive heating would occur often in the case of the food material having a small weight if controlled by the gas sensor and, therefore, arrangement is made to terminate the cooking early by relying on the weight. The utilization of the gas and weight sensors in the microwave heating discussed above is such that one of them is used as an auxiliary limiter to the other of them, and both are simultaneously utilized only when the food material is extremely small or under such circumstances.
In the heating apparatus according to the present invention, both the gas sensor and the weight sensor are effectively utilized, and it is so constructed that a base heating time T.sub.(W) appropriate to the weight of a food material and an added heating time T.sub.(.DELTA.H) are determined by the weight sensor and the gas sensor, respectively, the sum of the base heating time and the added heating time, that is, T.sub.(W) +T.sub.(.DELTA.H), representing the total cooking time T.sub.total during which the actual cooking is performed. With this construction, it has now become possible that change in heating time with the weight of the food material can be adjusted by the base heating time T.sub.(W), whereas change in heating time with the type of the food material and/or the shape of the vessel can be adjusted by the added heating time T.sub.(.DELTA.H).
Moreover, in the present invention, change in heating time which has resulted from the type of cake is adjusted by the gas sensor. Conventionally, there is an example wherein in a warming mode of the automatic cooking by the use of the microwave heating technique, the gas sensor is used to determine the type of a food material and then to adjust the heating time. According to this method, the rate of change of a detection output from the gas sensor generated during the heating operation is measured so that the type of a food material can be discriminated in the light of the measured value and the cooking time is subsequently adjusted by varying the value of detection level. However, this method cannot be utilized in the oven cooking of cakes or the like, because, while the oven cooking is carried out only by increasing the temperature inside the heating chamber, change of the temperature being increased takes place slowly with the rate thereof being small, requiring a relatively long time to heat the food material to a required temperature. Also, in order to adjust the temperature inside the heating chamber, a heating means such as a heater is repeatedly switched on and off. As a matter of course, much vapor is produced when the heater is switched on, but little vapor is produced when it is switched off. Influenced by the on and off switching of the heater, the rate of change of the vapor detected by the gas sensor fluctuates. Because of this, when the type of food material is to be discriminated depending on the rate of change of the vapor generation, no difference can be ascertained in type because the rate of change as a whole is small, and accurate discrimination cannot be achieved because of fluctuation of the rate of change. The present invention has been devised with regards paid to these problems and makes use of the amount of change, not the rate of change, in adjusting the cooking time peculiar to a particular cake.
As hereinbefore discussed, the establishment of a new technology necessary to automate the oven cooking of cakes or the like has been longed for.